Symmetrical component system



June 19, 1934. E. FRIEDLKNDER El AL 1,963,195

SYMMETRICAL CQMPONENT SYSTEM Filed March 2, 1932' Iii/ 2 I INVENTORS Eric/1 I'rzbdlanaer and a m @WM a a a WITNESSES:

Patented June 19, 1934 UNITED STATES PATENT OFFICE SYMMETRICAL COMPONENT SYSTEM vania Application March 2, 1932, Serial No. 596,258 In Germany March 3, 1931 8 Claims.

The present invention is directed to an improved method and means for segregating the symmetrical components of one or more electrical quantities from an electrical system. The invention is broadly similar to our copending application, Serial No. 554,140, filed July 30, 1931.

In accordance with the theory of symmetrical components, the rotational components of an electrical quantity may be segregated from any polyphase system by means of properly designed impedance networks, and many modifications of impedance networks are well known in the art. In all such prior art impedance network circuits, the energizing transformers associated therewith were connected by means of some metallic electrical connection thereby introducing the disadvantage that such transformers cannot be utilized for other burden control purposes.

In the above noted copending application are disclosed several modifications of impedance networks, or phase sequence segregating networks, wherein only an inductive or non-galvanic connection is provided between the energizing transformers associated with the phase sequence segregating network. In addition, the transformers are so arranged that the secondaries thereof constitute a portion of the impedance network, with the result that the actual number of elements required in the impedance network is materially v reduced.

The present invention is directed to several mod'fications of such phase sequence segregating networks and these modifications offer the distinct advantage of providing reliable and accurate indication of balanced or unbalanced conditions occurring in a polyphase electrical system.

One object of the present invention is, therefore, to provide a simplified phase sequence network for segregating the rotational components of an electrical quantity from a polyphase electrical system.

Another object of the present invention is to arrange the energizing means for a simplified phase sequence segregating network in such a. manner that only an inductive coupling is eflected between the respective energizing means.

A further object of the present invention is to provide a simplified phase sequence segregating network incorporating novel connections which provide a compensating means for the errors inherent in the energizing means for such network.

Further objects and advantages of the present a invention will become readily apparent from a consideration of the various figures included in the attached drawing, wherein Figure 1 is a schematic diagram of a simplified phase sequence segregating network and energizing means therefor, associated with a polyphase electrical system.

Fig. 2 is a vectorial representation of the electrical characteristics resulting from the use of the network arrangement of Fig. 1;

Fig. 3 is a diagrammatic view of a modified form of a phase sequence segregating network employing only an inductive coupling between the energizing means associated with the phase sequence segregating network and wherein the network connections are so arranged as to provide a compensating means for the errors inherent in the energizing means.

Fig. 4 illustrates a modified network arrangement corresponding to the Fig. 3 modification, and

Fig. 5 is a vectorial representation of the electrical characteristics resulting from the network arrangement of Fig. 4.

It is well known that the unsymmetrical current or voltage of a three phase system may be resolved into two component symmetrical systems rotating in opposite directions. These symmetrical systems have been arbitrarily termed positive phase-sequence and negative phase-sequence, respectively. In using such terminology, the positive phase-sequence components are considered to be the rotational components present in a balanced three phase system, while the system of negative phase-sequence components are only present in an unbalanced three phase system.

For the purposes of the present invention, only three phase ungrounded systems will be considered and no reference will be made to the occurrence of zero sequence or ground currents occurring in any polyphase system. In a three phase ungrounded system, only the positive phase-sequence components of current and voltage exist during balanced conditions and upon the occurrence of any unbalance, both the positive and the negative phase-sequence components of current and voltage are present; the ratio of the negative phase-sequence components to the positive phase-sequence components being in direct proportion to the degree of unbalance and the impedance characteristics of the system.

Referring more particularly to Fig. 1 of the drawing, a phase-sequence segregating network is illustrated as being adapted to segregate either the positive or the negative phase-sequence components of voltage from a three phase system.

In this figure, a voltage transformer 1 has the primary winding 2 thereof connected across phases A and B of a three phase ungrounded system 3. The secondary winding 4 of the transformer 1 has one terminal thereof connected to the primary winding 6 of a high reluctance transformer 7 and through an ohmic impedance 8 back to the remaining terminal of the secondary winding 4. The values of the inductance 6 and the ohmic impedance 8 are so chosen that the secondary voltage of the transformer l is resolved into two components, one of which is displaced 60 electrical degrees from the system voltage across the phases A-B.

The secondary winding 9, of the transformer '7, has one terminal thereof connected in series with the winding 11 of a relay 12, the secondary winding 13 of a voltage transformer 14 and thence to the remaining terminal of the secondary winding 9. The primary winding 16, of the transformer 14, is connected across the phases 13-0 of the polyphase system 3.

The transformation ratio of the intermediate transformer 7 is made one-to-two with the result that the winding 11 of the relay 12 is either fully energized or completely deenergized under balanced system conditions depending upon the connection of the primary and secondary windings of the energizing voltage transformers l and 14.

Assuming the voltage transformers 1 and 14 to have the primary windings thereof so connected to the polyphase systems 3 that the positive phase sequence components of voltage may be segregated therefrom, the relay winding 11 will be fully energized to close the contacts of relay 12 under balanced conditions existing on the system 3. However, assuming a predetermined degree of unbalance to exist on the system 3, the relay winding 11 would be ineffectively energized and the contacts thereof would not be closed.

Conversely, if the primary winding of the voltage transformers 1 and 14 are so connected to the polyphase system 3 that the negative phasesequence components of voltage may be segregated therefrom, the energizing winding 11 of relay 12 would be deenergized under balanced conditions existing on the system 3 and would only be effectively energized upon the occurrence of a predetermined unbalance on the system.

Obviously, the relay 12 may be replaced by a suitable indicating instrument and the illustration of the relay 12 is to be understood as generic in character and as representing any type of instrument responsive to unbalanced conditions on the polyphase system 3.

Assuming the voltage across the phases A-B to be represented by the vector E1, the voltage across the phases BC to be indicated by the vector E2 and the voltage across the phases A-C to be represented by the vector E3, the theory of operation of the scheme of Fig. 1 will be explained with reference to the vector diagram of Fig. 2.

In Fig. 2, the voltage vectors E1, E2 and E3 are indicated as being 120 electrical degrees d splaced and such vectors are representative of the phase voltages of the system 3, under balanced conditions. The voltage E1 is obtained by means of the voltage transformer 1 and such voltage is resolved nto two component parts by means of the inductance or transformer primary winding 6 and the ohmic impedance 8. Since the inductance 6 resolves the voltage vector E1 into a component which is displaced 60 electrical degrees therefrom, this resolved component is indicated by the vector E1 and the voltage drop in the ohmic impedance 8 is indicated by the vector E1.

The voltage provided by the voltage transformer 14 is indicated by the voltage vector E: and such voltage is impressed across the energizing winding 11 of relay 12 in series with the secondary winding 9 of the intermediate transformer 7.

As the transformation ratio of the intermediate transformer '7 is one-to-two, a voltage is induced in the secondary winding 9 which is in phase with, and double the magnitude of, the voltage impressed across the inductance or primary winding 6.

With reference to the vector diagram of Fig. 2, it may be noticed that the voltage component H1 is one-half the magnitude of the voltage voctor and 180 electrical degrees displaced therefrom. Since the voltage induced in the secondary winding 9, of the intermed'ate transformer 7, is in phase with and double the magnitude of the voltage component E1, the resultant voltage impressed across the energzing winding of relay 12 is zero, inasmuch as the voltage provided by voltage transformer 14 is represented vectorially by the voltage vector Obviously, in accordance with the vector diagram of Fig. 2, it may be noted that a resultant voltage will be impressed on the energizing winding 11 of relay 12 only when an unbalance occurs between the voltage vectors E1 and E2 or between voltages of phases 11-45 and B-C. This follows because of the fact that under any such unbalanced conditions, the voltage vectors E1 and no longer equal and displaced by angles of 120 with respect to each other. This results in the voltage E'i being of different magnitude and/ or phase position with respect to the voltage vector E2 thereby providing a resultant energizing voltage for the w'nding 11 of relay 12.

By interchanging either the primary or secondary wind'ngs of one of the voltage transformers 1 or 14, the winding 11 of relay 12 may be made to respond to the positive or negative phase-sequence components of voltage of the system 3, as desired. The provision of the intermediate transformer 7 effects only an inductive coupling between the voltage transformers 1 and 14 and also constitutes an element of the phasesequence segregating network, thereby smplifying the phase-sequence segregating network and allowing other burdens to be supplied by the voltage transformers 1 and 14.

Referr'ng now to Fig. 3, of the drawing, a voltage transformer 17 has the primary winding 18 thereof connected across the phases A--B of a three phase system 19 and the secondary winding 21, of the voltage transformer 17, is connected in a series c rcuit substantially similar to the series circuit for the voltage transformer 1 of Fig. 1. This series circuit comprises a series connected variable induct ve impedance 22 and an ohmic impedance 23. A second voltage transformer 24 has the primary winding 26 connected across the phase BC of the system 19 and the secondary winding 27 of the transformer 24 is inductively coupled with the impedance network assoc ated with the voltage transformer 17. r

The inductive coupling of the voltage transformers 17 and 24 is effected by means of an add tional voltage transformer 28 which has the primary winding 29 thereof connected across the secondary winding 27 of voltage transformer L spective voltage transformers. tion, the voltage transformer 1'7 is associated half of the voltage vector E2.

24 and the secondary winding 31 thereof connected across the variable inductive impedance 22 through a series connected indicating instrument 32.

The series connected variable inductive impedance 22 and the ohmic impedance 23 resolve the voltage vector E1 into the component vectors E1 and E1" as illustrated in Fig. 2. The variable connection associated with the inductive impedance 22 and the secondary winding 31 of voltage transformer 28 are so arranged that a voltage is impressed across the indicating instrument 32. This voltage is in phase with the voltage component vector E1 and may be varied in magnitude by changing the variable connection associated with the inductive impedance 22.

As the transformation ratio of the transformer 28 is two-to-one, the voltage of the secondary winding 31 is in phase with the voltage corresponding to vector E2 and equal to half the latter voltage. Obviously, under balanced conditions existing on the polyphase system 19, the indicating instrument 32 is deenergized since the voltage component vector E1 fully compensates for one It follows, therefore, that the indicating instrument 32 will be energized only upon the occurrence of unbalanced condition of the polyphase system 19 such that the relative phase positions and magnitudes of the voltage components El and E2 are altered from their normal balanced positions.

In Fig. 3 modification, either the primary or secondary terminals of one of the voltage transformers 1'7 or 24 may be interchanged to thereby provide for the energization of the indicating instrument 32 in accordance with the positive phase-sequence components of voltage occurring in the system 19.

The voltage transformer 28 effects the double function of providing an inductive coupling between the voltage transformers 1'7 and 24 and also of constituting an element of the phase-sequence segregating network. The double function of this transforming means is of great importance in that the impedance network is simplified and the voltage transformers 1'7 and 24 may be utilized to supply voltages for other control or metering devices.

The variable connection associated with the inductive impedance 22 permits the adjusting of the voltages impressed across the indicating instrument 32 and such adjustment permits the compensation for possible errors due to incorrectly calibrated ratios of transformation of the various voltage transformers.

Fig. 4 shows a modification of the arrangement shown in Fig. 3 and illustrates the possibility of interchanging the voltage energization of the re- In this modificawith the phases BC of the polyphase system 19 while the voltage transformer 24 is associated with the phases AB of the system. Because of this connection of the transformers 1'7 and 24, the voltage E2, corresponding to the phase voltage B-C, is resolved into the two component voltages E2 and E2" by means of the series connected ohmic impedance 23 and the inductive impedance 22. Inasmuch as the voltage induced 1 strument 32 is connected in series with the secondary winding 31 and across the ohmic impedance 23.

This arrangement provides for the deenergization of the indicating instrument 32 under balanced conditions existing on the system 19 inasmuch as the two voltages impressed across such instrument are 180 out of phase and are of the same magnitude.

In the Fig. 4 modification, an inductive coupling between the voltage transformers 1'7 and 24 through the phase-sequence segregating network is provided by means of the intermediate transformer 28, and such intermediate transformer also constitutes an element of the phasesequence segregating network. As pointed out with reference to the Fig. 3 modification, the primary or secondary terminal connections of either the voltage transformers 17 or 24 may be interchanged to provide for the segregation of the positive phase-sequence components of voltage occurring in the system 19, and the indicating instrument 32 may be energized by such phasesequence components of voltage.

The present invention obviously need not be limited to the precise arrangement of the phasesequence segregating means and the energizing means therefor, as illustrated in the drawing, and it is desired that no limitations be imposed thereon other than as indicated in the appended claims.

We claim as our invention:

1. In combination with a polyphase system, a pair of potential transformers each energized in accordance with a separate phase condition of a polyphase voltage quantity of said system, a mutual inductance device having a pair of electrically separate windings, impedance means, conductors completing a network including said impedance means and said device and having electrically separate secondary circuits for said potential transformers, each of said secondary circuits being connected to a winding of said mutual inductance device, and an electroresponsive device connected to said network to respond to two electrical quantities each derived from a separate phase of said polyphase quantity, said two electrical quantities being equal and in phase under a predetermined symmetrical condition of said polyphase voltage quantity.

2. In combination with a three-phase alternating-current circuit, a first potential transformer and a second potential transformer each energized in accordance with a separate phase condition of a three-phase voltage quantity of said circuit, an impedance element, conductors completing a secondary circuit including the secondary winding of said first transformer and said impedance element, said secondary circuit having an impedance phase angle of substantially an ratio mutual inductance device having a winding of n1 turns responsive to a 60 displaced electrical quantity of said secondary circuit and a second electrically separate winding of n2 turns responsive to an in-phase secondary electrical quantity of said second potential transformer, said inphase quantity being times as large as said 60 displaced quantity under a predetermined symmetrical condition of said threephase voltage quantity, and an electrical device responsive to an electrical condition of a winding of said mutual inductance device.

3. In combination with a three-phase alternating-current circuit, a first potential transformer and a second potential transformer each energized in accordance with a separate phase condition of a three-phase voltage quantity of said circuit, an impedance element, conductors completing a secondary circuit including the secondary winding of said first transformer and said impedance element, said secondary circuit having an impedance phase angle of substantially 60, a two-to-one ratio mutual inductance device having a low voltage winding responsive to a 60 displaced electrical quantity of said secondary circuit and having an electrically separate high voltage winding responsive to an iii-phase secondary electrical quantity of said second potential transformer, said in-phase quantity being twice as large as said 60 isplsced quantity under a predetermined symmetrical condition of said three-phase voltage quantity, and an electrical device responsive to an electrical condition of a circm't of said mutual inductance device.

4. In combination with a polyphase alternatingcurrent circuit, a first potential transformer and a second potential transformer, conductors connecting the primary windings or" said transformers to said circuit to be enei zed in accordance with adjacent voltages of three-phase system of voltages of said circuit, an impedance element, conductors completing a secondary circuit including the secondarywinding of said first potential transformer and said impedance element, a two-to-one ratio insulating transformer ha .ing a low voltage winding responsive to a displaced voltage component of said secondary circuit and having a high-voltage winding responsive to an iii-phase secondary voltage condition of said second potential transformer, said secondary voltage condition being twice as large as said 6% displaced component under predetermined synnnetrical voltage condition of said circuit, and an electroesponsive device connected in series with a winding of said insulating transformer.

5. In combination with a polyphase system, a mutual inductance device having a pair of trically separate windings, impedance means, means completing a network including said impedance means and said device, said network having a pair of circuits each connected to a separate winding of said device and energized in accordance with a separate phase voltage derived from said system, and an electroresponsive Tr-n Cluedevice connected to said network to respond to two electrical quantities each derived from one of said phase voltages, said two electrical quantities being equal and in phase under a predetermined symmetrical polyphase voltage condition of said system.

6. In combination with a three-phase system, an impedance element, a mutual inductance device raving a pair of electrically separate Windings, means completing a network including said impedance element and said mutual inductance device, said network having a pair of circuits each connected to a separate winding of said device and energized in accordance with a separate phase voltage derived from said system, the algebraic sum of the impedance phase angles of said circuits being substantially and an electroresponsive device connected to said networl; to respond to two electrical quantities each derived from a separate one of said phase voltages, said two electrical quantities being equal and in phase under predetermined symmetrical polyphase voltage condition of said system.

7. In combination with a polyphase system, electroresponsive means, means for deriving two phase-to-pnase voltages from said system, means including an inductive and an ohmic. impedance for resolving one of said phase-to-phase voltages into two component voltages, means including a two-to-one ratio transformer for energizing said electroresponsive means in proportion to said other phase-to-phase voltage, and means for simultaneously energi ing said electroresponsivc means in accordance with one of said component voltages.

8. In combination with a polyphase system, electroresponsive means, means for deriving two phase-to-phasc voltages from said system, means including an inductive and an ohmic impedance for resolving one of said pliase-to-phase voltages into two component voltages, means including a two-to-one ratio transformer for energizing said electroresponsive means in proportion to said other phase-to-pnase voltage, and means for simultaneously energizing said electrorcsponsive means in accordance with one of said component voltages, said means including a variable control connection associated with one of said impedances for equalizing the two energizing voltages for said electroresponsive means under balanced system conditions.

ERICH FRIEDLANDER. OSKAR SCHMUTZ.

Lab 

